The present disclosure is directed to an insert for use in drill bits, and especially to a drill bit insert featuring a crown on the insert capping the exposed end, and further incorporating a crown which is located under a PDC layer placed on the insert. The PDC layer is a layer of polycrystalline diamond which is shaped and contoured to a specified shape, and which forms a layer of very substantial hardness.
The insert of the present disclosure is fabricated of very hard metal, and is typically formed of various types of carbides. Among the harder carbide materials, the preferred form of insert construction is cobalt based tungsten carbide (WC) which provides a strong and vibration resistant body. It is hard, substantially as hard as any metal that can be fabricated. Moreover, the tungsten carbide insert is constructed so that it has a binding material in it to hold together tungsten carbide particles thereby yielding a composite material insert.
The outer end of the insert is crowned with a PDC layer. This refers to the layer of material which is crystalline in structure and which is formed of diamond material. It is a composite material with a binding agent mixed with small chips of crystalline nature. It is typically made from synthetic diamonds. These industrial grade diamonds are mixed small particles shaped in a mold so that the mold provides the desired shape to the finished product. If need be, the cap is molded in place on the insert. Further the small pieces of crystalline material are bonded together so that the whole of the structure has the form of a shock resistant cap on the end of the insert which is able to endure the rough conditions that occur during use of the drill bit having the insert installed in the bit body.
The insert of the present disclosure is formed as a right cylinder of circular cross section. The insert is elongate, having one end which is forced into a hole in the drill bit body. It is anchored in the bit body in an interference fit or by brazing to assure that it stays in the bit body. Thus anchored, the insert positions at a specified location the remote end which is contacted against formations making up the crust of the earth during drilling of an oil well. During drilling, the insert is jammed against the formation, and tends to either crush or gouge the facing materials while advancing a drilled hole. The remote end of the insert is exposed to scraping action against the formations of the earth and tends to be worn from scraping. As wear occurs, the wear grinds away the end portion. For that reason, the end is provided with the PDC cap. A representative prior art device is set forth in previously issued U.S. Pat. No. 4,109,737. This shows an insert installed in a drill bit body. The insert is provided with a crown formed of bonded diamond material on the end of the insert. More specifically, in FIG. 4a and also FIG. 4c of that disclosure, inserts are shown which extend over the exposed end face of the insert. The devices of the '737 patent are the prior art which has been used with some measure of success heretofore but which now represent the old way of doing things in the drill bit art. The insert of the present disclosure provides improvements over the referenced inserts of the '737 patent.
In one aspect, the present disclosure is drawn to and directs attention to a longer insert which is sufficiently long that it has an end which is exposed for drilling by striking on the wall surface in the well borehole. Whether the drilling action is described as chipping or gouging, the cutting action is accomplished by the long ended insert. The wear and tear of use is occasioned at the PDC crown. The crown in the present apparatus is protected from delamination which is a mode of failure which occurs when shear loading chips off a corner, thereby forming a break which may propagate across part or all of the PDC crown. The present disclosures sets forth a mechanism which overcomes that risk. Moreover, this disclosure describes a particular arrangement in which the PDC crown is shaped so that destruction does not occur in that fashion.
In one aspect of the present disclosure, a single protruding enlargement is integrally constructed in the unmodified insert, and this insert is then crowned or capped. This enables the enlargement to hold in place so that the PDC layer does not delaminate or otherwise fail in a catastrophic manner. Large scale failures are avoided by this approach. Large scale failures especially occur when the end layer is a substantially thick PDC layer which tends to be brittle, and which is not modified by the incorporation of or the inclusion of the necessary protective grasp between the WC insert body and the PDC crown attached to it.